The measurement of properties of liquid and gaseous fluids by detecting a voltage produced by a sensor is a common problem in research and in industrial processes. The measurement of ion concentrations of fluid solutions is a typical example and utilizes ion selective electrodes having one or more electrodes which are immersed in a chemical solution.
In one common type of ion selective electrode, the ion concentration is sensed by an electrode having a glass membrane. A tube is attached to the membrane and is filled with a filling solution. A metal wire is inserted in the top of the tube to provide an electrical contact to the filling solution. The filling solution must be hermetically sealed inside the tube and, a hermetic seal is typically made by melting the tube until it collapses around the metal contact after the tube has been filled with the solution.
As will be discussed in more detail below, present methods for fabricating the electrode, especially the making of the seal, require glass workers with a high degree of skill. Furthermore, even with highly skilled workers, a significant number of defective electrodes is to be expected.